The present invention relates to a pressure regulator assembly and, especially, to a pressure regulator assembly for use with a breathing apparatus in an environment containing highly toxic substances.
A self contained breathing apparatus (“SCBA”) is a device used to enable breathing in environments which are IDLH—immediately dangerous to life and health. For example, firefighters wear an SCBA when fighting a fire. The SCBA typically has a harness containing an air tank which is connected to a facepiece, all of which are worn or carried by the user. The tank typically contains air or gas under high pressure (2200 psi-4500 psi) and is connected to a first stage regulator which reduces the pressure to about 80 psi. The SCBA usually has a second stage regulator that has an inlet valve which controls the flow of air for breathing between the air tank and the facepiece. The valve controls the flow of air through the regulator in response to the respiration of the user. Such respiration-controlled regulator assemblies are disclosed, for example, in U.S. Pat. Nos. 4,821,767 and 5,016,627.
Typically, a diaphragm divides the regulator assembly into an inner chamber having a pressure corresponding to the pressure within facepiece of the SCBA and an outer chamber having a pressure corresponding to the surrounding environment, which is typically ambient pressure. The diaphragm is coupled to an actuating mechanism which opens and closes the inlet valve. The user's respiration creates a pressure differential between the inner and outer chambers of the regulator assembly which, in turn, causes displacement of the diaphragm thereby controlling (i.e., opening and closing) the inlet valve mechanism. As a result, such regulators are often called pressure demand regulators.
The facepiece of the SCBA is preferably maintained at a positive pressure as compared to the surrounding environmental pressure to prevent toxic gases and vapors in the environment from entering the facepiece. This positive pressure can, for example, be facilitated by biasing the diaphragm with a spring.
The positive pressure within the facepiece, however, may not be sufficient by itself to protect the user against unusually high concentrations of certain chemical and biological agents such as sarin (C4H10FO2P, an extremely toxic chemical warfare agent that is a powerful cholinesterase inhibitor) or mustard agent (C4H8Cl2S, an irritant vesicant oily liquid used especially as a chemical weapon). Although SCBAs are primarily constructed from thick-walled plastic, metal and rubber components, the diaphragm in the regulator assembly is often fabricated from an elastomeric material that is sufficiently porous and/or permeable to such highly toxic agents to allow dangerous levels thereof to enter the breathing system.
It is desirable, therefore, to develop a pressure regulator assembly suitable for use in environments including such highly toxic agents.